Implantable medical sensors are used for sensing physiological signals in a patient for use in diagnosing a disease state or managing patient therapies. Among examples of implantable sensors are pressure sensors, flow sensors, acoustical sensors, and optical sensors. A pressure sensor positioned in the heart or in a blood vessel is highly useful in monitoring cardiovascular conditions, such as heart failure, hypertension, arrhythmias or other conditions. For example, a capacitive pressure sensor includes one capacitor electrode along a diaphragm and a second capacitor electrode substantially parallel to and held a few micrometers from the electrode of the diaphragm. An “air gap” provides insulation between the two parallel electrodes. As the blood pressure changes, the diaphragm flexes closer to or further away from the second electrode, resulting in a change in capacitance. The capacitance can be measured in many ways and can be converted to pressure using a calibration algorithm.
Some sensors can produce a baseline signal that drifts over time or presents a baseline offset. The causes of drift or offset can vary and lead to erroneous measurements determined from the sensor signal, particularly for calibrated sensors such as a calibrated pressure sensor. Accordingly, sensor designs are needed that reduce the potential for error in chronically implanted sensors.
In the present disclosure, sensor designs that reduce the potential for error in chronically implanted sensors are disclosed.
In one embodiment, an implantable medical device is disclosed that comprises a housing having an outer wall and comprising an inner shell and an outer layer formed to extend over and enclose the inner shell to form the outer wall, the outer layer having an inner side engaged against the outer wall of the inner shell and having a thickness extending between the inner side and the outer wall of the housing, wherein the inner shell and the outer layer form a flat portion. The implantable medical device includes a flexible diaphragm that is formed within the inner shell along the flat portion, and the outer layer may include a recessed portion formed along a length of the outer layer between the diaphragm and the inner side, with the thickness of the outer layer adjacent to the diaphragm being greater than the thickness of the outer layer extending over the diaphragm.
In accordance with another embodiment, an implantable medical device is disclosed that comprises a housing having an outer wall and comprising an inner shell and an outer layer formed to extend over and enclose the inner shell to form the outer wall, the outer layer having an inner side engaged against the outer wall of the inner shell and having a thickness extending between the inner side and the outer wall of the housing, wherein the inner shell and the outer layer form a flat portion. The implantable medical device includes a flexible diaphragm formed within the inner shell along the flat portion, with the outer layer including a recessed portion formed along a length of the outer layer between the diaphragm and the inner side, and with the thickness of the outer layer adjacent to the diaphragm being greater than the thickness of the outer layer extending over the diaphragm. Continuing with the embodiment, a channel is formed in the outer layer that extends from an opening formed at the outer wall, through the outer layer to an opening formed along the inner side of the outer layer extending along the flat portion.
In accordance with another embodiment, an implantable medical device lead is disclosed. The lead comprises an elongated lead body and has a housing having an outer wall and comprising an inner shell and an outer layer formed to extend over and enclose the inner shell to form the outer wall, the outer layer having an inner side engaged against the outer wall of the inner shell and having a thickness extending between the inner side and the outer wall of the housing such that the inner shell and the outer layer form a flat portion. The implantable medical device lead further includes a flexible diaphragm that is formed within the inner shell along the flat portion with the outer layer including a recessed portion formed along a length of the outer layer between the diaphragm and the inner side, and with the thickness of the outer layer that is adjacent to the diaphragm being greater than the thickness of the outer layer extending over the diaphragm.
In accordance with another embodiment, an implantable medical device lead is disclosed that comprises an elongated lead body and a housing having an outer wall and comprising an inner shell and an outer layer formed to extend over and enclose the inner shell to form the outer wall, the outer layer having an inner side engaged against the outer wall of the inner shell and having a thickness extending between the inner side and the outer wall of the housing, wherein the inner shell and the outer layer form a flat portion. The implantable medical device lead also includes a flexible diaphragm formed within the inner shell along the flat portion with the outer layer including a recessed portion formed along a length of the outer layer between the diaphragm and the inner side, and wherein the thickness of the outer layer adjacent to the diaphragm is greater than the thickness of the outer layer extending over the diaphragm. The implantable medical device lead further includes a channel formed in the outer layer, the channel extending from an opening formed at the outer wall, through the outer layer to an opening formed along the inner side of the outer layer extending along the flat portion.